We present a case of a
25-year-old woman with multiple blackouts and no structural heart
disease, with abnormal T-U waves and borderline QT interval on her
resting electrocardiogram. During emotional stress she developed
frequent monomorphic ventricular premature beats, with characteristic
changes of the sinus complexes immediately following the premature
beats, namely augmentation and greater degree of merging of the T and U
waves and QTc interval prolongation. The changes alert about the
possibility of congenital long QT syndrome, specifically genotype 2 or
1.

Figure 1 presents a resting
electrocardiogram (ECG) recorded at 25 mm/sec, 10 mm/mV in a
25-year-old woman with a history of multiple blackouts. It shows sinus
rhythm, heart rate of 80 beats per minute, notched T wave in lead V2,
and abnormal augmented U wave in leads V2 to V4. The QT interval
measured to the T-U nadir is 383 ms (manual measurement with on-screen
calliper) and the QTc interval (correction by Bazett's formula) is
borderline prolonged at 442 ms.

Figure
1 Resting ECG in a 25-year-old woman with daily blackouts. See
the text for details.

The ECG
presented in Figure 2 was
recorded in the same patient few minutes later, apparently during
emotional stress (she was awaiting ajmaline test to exclude Brugada
syndrome, and has just been told that there was a risk of 1 in 200 of
inducing an arrhythmia during the test that would need an electrical
shock to be stopped). The average heart rate is 106 beats/minute and
every forth beat is a ventricular premature beat (VPB) (pattern of
quadrigeminy). The T-U wave of each sinus beat immediately following a
VPB is augmented and with a greater degree of T-U merging compared to
the T-U wave of the next sinus beat. The QT interval of the 1st
post-VPB sinus beat measured to the T-U wave nadir is 396 ms and the
corrected QTc is prolonged at 528 ms, although precise measurement
seems difficult.

Figure 2 Resting ECG recorded in the same patient during
emotional stress. See the text for details.

In Figure 3 (right panel), the ST-TU
waves of the 4 sinus complexes immediately following a VPB (black
lines) and of the next 4 sinus beats (grey lines) have been
superimposed to demonstrate the post-VPB augmentation of the T-U wave.
In Figure 3, left panel, all sinus complexes of the resting ECG
presented in Figure 1 have been superimposed for comparison.

Figure 3 Left panel: All QRS-T
complexes in lead V4 of the ECG presented in Figure 1 have been
superimposed and aligned by the QRS complex. Right panel: The 4 QRS-T
sinus complexes in lead V4 immediately following a ventricular
premature beat (black lines) and the next 4 QRS-T sinus complexes (grey
lines) have been superimposed and aligned by the QRS complex to
demonstrate the difference in the T wave shape. The scale is arbitrary.
See the text for details.

The borderline
QT prolongation with abnormal T and U waves in a symptomatic young
female patient alerts about the possibility of congenital Long QT
Syndrome.1 The ECG during
emotional stress displays features characteristic for this condition
(specifically genotype 2 or 12):
further prolongation of the QTc interval and augmentation of the
abnormal U wave with T-U merging of the immediate post-extrasystolic
sinus beats.3